Nuclear migration and positioning are fundamental processes required for proper development, cell polarization, fertilization, cell motility, meiosis and fertilization, as well as cell division. An understanding from a molecular and genetic perspective of how nuclear migration and positioning are accomplished will lead to greater insight into cellular organelle positioning in general, as well as potential therapeutic targets fo a number of heritable human diseases. The experiments proposed here are expected to lead to the discovery and characterization of novel pathways that function parallel to the SUN (UNC-84) and KASH (UNC-83) nuclear-envelope bridge that moves nuclei. I will undertake genetic and cellular approaches to analyze the phenotypes and molecular identities of emu (for the enhancer of the nuclear migration defect of unc-83/84) mutants. One emu gene (fln-2) was identified as a divergent filamin A homolog. Filamins are conserved cytoplasmic proteins that organize the actin cytoskeleton and are involved in diverse cellular processes including cell signaling and mechanotransduction, regulation of cellular architecture, and have recently been shown to regulate nuclear shape in cultured mouse cells. In humans, heritable diseases caused by mutations in filamin genes lead to various diseases of the major organ systems. The overall central hypothesis of this proposal is to characterize novel pathways required for nuclear migration using the model system C. elegans. In order to accomplish this, a combination of forward genetics and whole genome sequencing will be used to identify the molecular basis of the lesions in the emu candidates. To more fully understand emu nuclear migration defects, a live cell imaging system will be developed, which is expected to advance our understanding of nuclear migration in a developing organism. As an example of an analysis of the cellular role of an emu gene, the cellular roles of FLN-2 during P-cell nuclear migration will be examined. The proposed study is innovative and significant because of the strengths of our model system. Most importantly, the results are expected to determine how emu genes function in nuclear migration in the context of a living organism. These results will significantly advance the field by elucidating novel pathways required for nuclear migration. The proposed activities will lead to a better understanding of how nuclear migration is accomplished at the cellular and molecular levels and potentially shed mechanistic insights into the pathogenesis of heritable diseases caused by mutations in genes required for nuclear migration and positioning.